CVE-2026-100780 in Firefox
Summary
by MITRE • 09/29/2026
Use-after-free in the DOM: Core & HTML component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
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Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability represents a critical memory management error within the Document Object Model core and HTML components of Mozilla Firefox browsers, specifically classified as an use-after-free condition. This type of flaw occurs when software continues to reference a memory block after it has been deallocated or freed by the system. In the context of browser rendering engines, this typically involves complex interactions between JavaScript execution contexts and DOM node lifecycle management. When a script manipulates DOM elements, removes them from the document tree, or triggers garbage collection routines, the underlying C++ code may fail to properly invalidate pointers or references that still point to the now-deallocated memory region. This creates a window of opportunity where subsequent operations attempt to read from or write to this invalid address space rather than allocating new valid memory for the object in question.
From a technical perspective, use-after-free vulnerabilities are particularly dangerous because they allow an attacker to control the content that is written into freed memory if they can influence what gets allocated at that specific location before it is reused. This mechanism often leads to arbitrary code execution with the privileges of the browser process. An attacker could craft a malicious webpage containing specially designed HTML and JavaScript payloads that trigger the premature freeing of DOM nodes while maintaining active references through event handlers or asynchronous callbacks. When these dangling pointers are dereferenced, they may overwrite critical data structures such as function pointers or virtual table entries within the browser's memory space. This corruption can redirect execution flow to attacker-controlled shellcode embedded in adjacent heap allocations, effectively bypassing modern exploit mitigation techniques like Data Execution Prevention and Address Space Layout Randomization if not properly configured or circumvented through additional primitive exploitation steps.
The operational impact of this vulnerability is severe, as it enables remote code execution without requiring any user interaction beyond visiting a maliciously crafted website. Since the flaw resides in core DOM and HTML processing components, it affects all standard browsing activities involving dynamic content manipulation. Users who navigate to compromised or attacker-controlled sites could have their systems fully compromised, leading to data theft, installation of persistent malware, or use as part of a botnet. The vulnerability persists across multiple versions including Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17 until the specific patches are applied. This broad version impact highlights the systemic nature of the defect within the rendering engine's memory management logic rather than an isolated incident in a single feature module.
Industry standards categorize this flaw under CWE-416, which defines use-after-free errors as a subset of improper resource cleanup vulnerabilities that lead to undefined behavior and potential security breaches. In terms of attack vector classification according to MITRE ATT&CK, this vulnerability aligns with techniques involving memory corruption exploitation, specifically those leveraging heap spraying or arbitrary write primitives to achieve code execution. The remediation strategy involves applying the provided software updates which contain fixes for the reference counting mechanisms in the DOM implementation. These patches ensure that object lifecycles are strictly managed and that pointers are nullified upon deallocation to prevent dangling references from being accessed. Organizations should prioritize patching all affected Firefox installations immediately, particularly those used by high-value targets or connected to sensitive networks, while also enforcing strict content security policies to mitigate the risk of executing untrusted scripts that might trigger such memory corruption scenarios.